The dynamics of magnetically trapped fluids. I - Implications for umbral dots and penumbral grains

Abstract

view Abstract Citations (82) References (64) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Dynamics of Magnetically Trapped Fluids. I. Implications for Umbral Dots and Penumbral Grains Choudhuri, A. R. Abstract A study of the magnetohydrodynamic system in which a nonmagnetized fluid in a gravitational field is surrounded by a fluid carrying a vertical magnetic field is presented. It is pointed out that this study can throw some light on the fine-structural features of a sunspot. The equilibrium configuration of the field-free fluid is a tapering column ending at an apex. The regions away form the apex can be studied by the slender flux tube approximation. A scheme developed to treat the apex indicates that, just below the apex, the radius of the tapering column opens up with a 3/2 power dependence on the depth below the apex. If the internal pressure of the field-free fluid is increased, the apex rises, and a static equilibrium may not be possible beyond a limit if the magnetic pressure drops quickly above a certain height. The nature of steady-flow solutions beyond this limit is investigated. Under conditions inside a sunspot, a column of field-free gas is found to rise with a velocity of about 100 km/hr. If umbral dots and penumbral grains are interpreted as regions where the field-free gas ultimately emerges, a very natural explanation of most of their observed properties is obtained. Publication: The Astrophysical Journal Pub Date: March 1986 DOI: 10.1086/164042 Bibcode: 1986ApJ...302..809C Keywords: Magnetohydrodynamics; Solar Granulation; Solar Magnetic Field; Sunspots; Fluid Pressure; Incompressible Fluids; Magnetic Flux; Polytropic Processes; Steady Flow; Solar Physics; HYDROMAGNETICS; SUN: MAGNETIC FIELDS; SUN: SUNSPOTS full text sources ADS |